Headphones are used to play audio for users of electronic devices with media playback capabilities. For example, a pair of headphones may be used to play music for a user of a media player or may handle audio for a cellular telephone user.
Traditional headphones have relatively large ear cups. More recently, smaller headphones known as earbuds have been developed. In some earbud-style headphones, a small plastic earpiece rests in the outer ear canal of the user. Other earbuds have elastomeric earpieces that fit snuggly within a user's ear canal.
Earbuds are used in a variety of environments. For example, earbuds may be plugged into computers or other electronic equipment that is powered from a wall outlet. Earbuds are also used in static-filled environments such as airplanes. Earbuds are sometimes handled roughly, so durability is a concern.
These possible operating environments impose constraints on earbud designers. For example, a durable earbud that is formed from metal parts may be susceptible to electrostatic discharge. Electrostatic charge develops on a user in the course of a user's normal activities. As static electricity builds up on a user's ear, an electrostatic potential can develop across insulating portions of an earbud such as an elastomeric earpiece. If the amount of charge that develops is large enough, an electrostatic discharge event will occur. During the electrostatic discharge event, charge buildup will be released as charge flows across the insulating portions of the earbud. This may produce a spark that is felt by the user or may produce an audible crackle as the charge interacts with the speaker driver in the earbud.
Sparks and audible interference can be unpleasant for users. Although some of these effects can be mitigated by forming earbuds entirely from plastic, conventional all-plastic earbud designs tend not to be aesthetically appealing and may not be sufficiently durable to withstand rough handling. Some conventional earbuds address the effects of electrostatic discharge events by shorting their positive audio lines to metal driver parts in the earbuds. This approach may not be optimal when the earbuds are used with wall-powered equipment, because the positive audio line could potentially become shorted to a live power supply line if the wall-powered equipment were to develop an electrical fault.
It would therefore be desirable to be able to provide earbuds that are able to safely mitigate the effects of electrostatic discharge events.